Apparatus for generating fusion reactions



Sept. 22, 1970 R. L. HIRSCH ET AL Filed April 24 1968 APPARATUS FORGENERATING FUSION REACTIONS 4 Sheets-Sheet 1 (AT/100E /ONSOUPCE ave/oNODE 27 THEPMION/c Tl/00E 25 F- 5.2 2 22 2L0 30 29 +600V 7 r, r r 3 U) 8-sl v A?A0/US\ INVENTORSZ Qoseszr L. HIESCH,

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APPARATUS FOR GENERATING FUSION REACTIONS Filed April 24 1968 4Sheets-Sheet 2 GENE A.Mes| s-,

, ATTORNEYS.

P 1970 R. HIRSCH ET 3,530,497

APPARATUS FOR GENERATING FUSION REACTIONS Filed April 24 1968 4Sheets-Sheet 5 Roaster L. HuescH. GENE A. MEEKS,

ATTORNEYS Sept. 22, 1970 sc ET AL 3,530,497

APPARATUS FOR GENERATING FUSION REACTIONS Filed April 24, 1968 4Sheets-Sheet 4 Zla.

INVENTOES! ROBERT L. HlRscH, GENE A.MEEI S, s0KV BY7M ATTORNEY3.

Patented Sept. 22, 1970 Int. Cl. G21b US. Cl. 176-1 9 Claims ABSTRACT OFTHE DISCLOSURE A generally spherical or cylindrical anode hasconcentrically positioned therein an ion-source grid and a cathode, bothgenerally spherical or cylindrical and permeable to charged particleflow. The grid is interposed between the anode and cathode, and thecathode is hollow, defining a volume centrally located with respect toall three of the anode, grid and cathode electrodes. This volume is freeof tangible structure. A fusion-reacting gas is contained within thevolume. A voltage is applied to the three electrodes for establishing afirst electric field in the space between the anode and grid and asecond electric field in the space between the grid and the cathode. Theion-source grid is at a positive potential with respect to both theanode and cathode. The second electric field is of sufficient magnitudeto impart fusion-reacting energies to particles of positive chargeintroduced into the second space. A thermionic cathode is positioned inthe first space between the anode and grid.

BACKGROUND OF THE INVENTION Field of the invention This inventionrelates to apparatus for generating fusion reactions, and moreparticularly to apparatus for producing controlled nuclear-fusionreactions with facility and reliability.

Description of the prior art In Farnsworth Pat. No. 3,258,402, issuedJune 28, 1966, as well as Farnsworth Pat. No. 3,386,883, issued June 4,1968 on application Ser. No. 549,849, filed May 13, 1966, there aredisclosed methods and apparatuses of the character with which thepresent invention is concerned, capable of producing continuous fusionreactions. Generally speaking, the apparatuses of these prior patentsutilize a spherical geometry in which two generally sphericalelectrodes, one a cathode and the other an anode, are concentricallypositioned with one inside the other. The cathode is electron-emissivein one embodiment of the aforesaid patents and is concentricallysurrounded by a shell-like anode. The cathode is permeable to the flowof ions, while the anode is not. In operation, an electrical discharge,composed of high-order magnitude electron and ion currents in the spaceenveloped by the cathode, produces a radial potential distributionwhich, generally speaking, is a minimum adjacent to the center of thecathode cavity and a maximum outwardly therefrom, the location of onesuch maximum being adjacent to the anode wall. Developed at a finiteradius intermediate the center and the cathode wall is a virtual anodein the form of a spherical sheath. The potential of this virtual anodeis essentially equal to that of the structural anode, thereby resultingin the entrapment of ions within the virtual anode sheath. By reason ofelectron emission from the cathode, the potential minimum is formed atthe center, which results in the trapped ions oscillating through thecenter. With a sufficiently high difference of potential between thevirtual anode and the center, the

trapped ions will be propelled at nuclear-reacting energies, so that ioncollisions occurring at the center produce nuclear-fusion reactions.

The ions of the bipolar charges which are utilized for generating theaforesaid virtual electrodes as well as the fusion reactions, in theapparatus of the aforesaid Farnsworth Pat. No. 3,258,402, are obtainedin one instance by ionizing neutral gas introduced directly into theanode itself and in another instance by means of ion guns located on theoutermost of the anode and cathode, these ion guns each producing apencil-like, solid, cross-section beam which is aimed at the center ofthe device. In Farnsworth Pat. No. 3,386,883, application Ser. No.549,849, mentioned hereinbefore, the source of the ions is generallyconfined to ion guns mounted on the exterior of the anode having acathode thereinside. These ion guns also produce beams of concentrated,pencil-like configuration of solid cross-section.

Experimental evidence has shown that the more nearly radial the ionmotions, the more efiicient will be the utilization of the ions inproducing fusion reactions. Ions not so reacting will represent a powerloss. It has been found that space charge spreading in the pencilion-beams mentioned hereinbefore produces a significant number ofnonradial ions, thereby resulting in less than maximum utilization ofthe total number of injected ions and a reduction in ion-trappingefficiency.

SUMMARY OF THE INVENTION In accordance with the broader aspects of thisinvention, there is provided an apparatus (sometimes referred to as afusor) for generating fusion reactions in which a spherical orcylindrical anode concentrically envelopes correspondingly shapedcathode and ion-source grid electrodes. The cathode encloses a volumefree of tangible structure and centrally located with respect to theother electrodes. Both the cathode and ion-source grid are permeable tothe flow of gas, including positively charged particles. The ion-sourcegrid is interposed between and spaced from the anode and cathode. Meansare provided for applying potentials to the three electrodes which establishes a first electric field in the space between the anode andion-source grid and a second electric field in the space between thegrid and the cathode. These potentials are so applied that theion-source grid is positive with respect to the anode. Also, thepotentials applied are such that the second electric field is ofsufficient magnitude to impart fusion-reacting energies to particles ofpositive charge introduced into the second space.

A sheath or shell-like cloud of electrons is caused to shroud theion-source grid, this cloud being developed primarily by means of athermionic cathode disposed in the space between the anode and theion-source grid. Electrons from this thermionic cathode oscillatethrough the openings in the ion-source grid, thereby contributing to theformation of the aforesaid cloud, such that collisions of cloudelectrons with neutral gas become imminent, resulting in the formationof ions inside the ion-source grid which are propelled toward thecentrally located cathode by reason of the potential difference. Theseions are essentially focused toward the center of the volume inside thecathode and interact via their space charge such that definiteprobability obtains for the collision of such ions at the center.

OBJECTS OF THE INVENTION It is an object of this invention to provideapparatus for generating fusion reactions in which ions may be createdin a substantially circular pattern of common radius about a centertherewithin such that ion streams crossing at the center emanatesubstantially from all points on the circular pattern.

It is another object of this invention to provide an apparatus forproducing fusion reactions in which an ionsource electrode is providedfor developing an area source of ions which encircles a center towardwhich the ions are directed for producing fusion reactions.

BRIEF DESCRIPTION OF THE DRAWINGS The above-mentioned and other featuresand objects of this invention and the manner of attaining them willbecome more apparent and the invention itself will be best understood byreference to the following descrip tion of an embodiment of theinvention taken in conjunction with the accompanying drawings, wherein:

FIG. 1 is a diagrammatic illustration of a conceptual embodiment of thepresent invention used in explaining the operation thereof;

FIG. 2 is a potential distribution curve used in explaining theoperation;

FIG. 3 is a side view, partly sectioned for clarity of illustration, ofone embodiment of this invention;

FIG. 4 is a similar view of a second embodiment of this invention;

FIG. 5 is a cross-section taken substantially along the section line 55of the embodiment of FIG. 4;

FIG. 6 is an end view of the embodiment of FIG. 4; and

FIG. 7 is a diagrammatic illustration of the arrangement of FIG. 4 usedin explaining the operation thereof.

DESCRIPTION Involved in this invention is a non-magnetic method for theconfinement of ionized fusion gases and the utilization of thisphenomenon for the construction of a controlled nuclear-fusion reactordiagrammatically illustrated in FIG. 1. An ion-permeable circularcathode is concentrically surrounded by a circular anode 21 and anion-source grid 22 interposed therebetween. The grid 22 as well as thecathode 20 have a high degree of openness to accommodate therethroughthe free flow of gas and charged particles. The grid 22 may behypothetically considered as uniformly emitting ions over the entirecircumference thereof. In practical embodiments of this invention, theshapes of these electrodes may be spherical, cylindrical or toroidal, aswill appear from the description that later follows.

With perfectly radial motions, ions from the grid 22 will be acceleratedinto the cathode 20, where mutual repulsion therebetween will cause themto be decelerated and brought to rest at some finite radius indicated bythe numeral 23. They will then be accelerated radially outwardly. Afterpassing through the cathode 20, they will again be brought to rest atthe grid 22. Since ions are born at a location radially outwardly fromthe circle 23, concentration of ions at that circle 23 can be referredto as a virtual anode.

More particularly, FIG. 1 illustrates an hermetically sealed sphericalelectron-tube structure in which the cathode 20 may be considered as anopen-mesh electrode formed of metallic screens or the like. The anode 21may be considered as a solid metallic shell impervious to the flow ofgas. The grid 22 may be considered as being of the same construction asthe cathode 20. Suitable electrical connections are made to theelectrodes 20, 21 and 22, a lead 24 being connected to the anode 21 forapplying a positive potential thereto from power source 26, another lead25 to the cathode 20 for connection to the negative terminal of thepower source 26, and still another lead 27 to the grid 22 for applying aslightly higher positive potential thereto than that on the anode 21,this slightly higher potential being provided by a power supply 28. Inthe preferred embodiment of this invention, the anode 21 is grounded. Athermionic cathode 29, preferably annular in shape as shown, is fixedlypositioned in the space between the anode 21 and grid 22, such thatelectrons therefrom will 4 flow toward the grid 22 rather than to theanode 21. The cathode 29 is grounded and otherwise has a filament supplyvoltage (not shown) connected thereto.

Ignoring for the moment the affect which the cathode 29 has upon theoperation of the device, a neutral gas at low pressure inside the grid22 is ionized. There develops, then, an electrical discharge composed ofhighmagnitude electron and ion currents in the volume inside the cathode20 which results in the development of a dilference of potential whichmay be controlled so as to be a minimum near the geometric center 30 anda maximum adjacent to the grid 22, with one or more potential maxima(virtual anodes) and minima (virtual cathodes) concentrically enclosedwithin the cathode 20. Energetic ions, falling inwardly toward thecenter 30 from regions of high potentials, will be propelled atvelocities (energies) which are sufiicient to produce nuclear-fusionreactions.

Ions born generally and uniformly adjacent to the inner surface of thegrid 22 are indicated by the numeral 31 as following the radial paths ofthe respective arrows 32 to the inner boundary of the virtual anode'indicated by the circle 23. This circle 23 is concentric with respect tothe center 30 and indicates the size and location of the virtual anode.

Electrons in the device created in a region radially outside the virtualanode 23 will be accelerated toward the latter, passing through ittoward the center 30. Once inside the virtual anode 23, mutual repulsiontherebetween will decelerate them until they produce a nega tive spacecharge at some smaller radius, indicated by the circle 34 whichrepresents a virtual cathode of spherical shape concentric about thecenter 30. Ions from the virtual anode 23 then will be acceleratedinwardly toward this virtual cathode 34. By proper adjustment of therelative ion and electron currents, this virtual cathode 34 can bemaintained at such a small radius that it can be regarded as beinglocated almost at the exact center 30. The ions 31 traveling throughthis center reg'ion will possess high kinetic energies. Many of theseions will collide, in this central region, producing fusion reactions.

The reason for forming the virtual electrodes 23 and 34 is theattainment of particle trapping or confinement at high density by forcedcharge separation in spherical geometry. Formation of the virtualelectrodes obviously consumes power, and the bipolar charges are theinstruments used in the virtual electrode formation. The moreetiiciently these instruments are used, the less the power consumed.This invention is directly concerned with these efficiencies and theprovision of an area source of ions which spherically encompasses thebipolar configuration in the center.

The ideal structure is diagrammatically shown in FIG. 1 in which theion-source grid 22 is considered as the area source of the ions 31 whichemanate from the entire spherical surface thereof. The ions areconsidered as following precisely radial paths such that uponencountering the virtual anode 23, they return to the grid 22 along thesame paths. Each ion therefore contributes all of its energy to theformation and retention of the virtual anode 23, such that the ions 31considered as instrumentalities are utilized with maximum efiicency. Incontrast, nonradial movements of the ions 31 will result in less thanmaximum efliciency in the utilization of the ions in the formation ofthe virtual anode 23, and any structure or forces which contribute tothese non-radial movements constitute deficiences which should beremedied. Nonradial space charge spreading between adjacent ions has inprior art devices produced these non-radial components. In the presentinvention, this space charge spreading is substantially eliminated bythe use of the spherically shaped ion-source grid 22, which may beconsidered as an area source of ions from which ions emanate over theentire spherical surface thereof. Ions in their radial motions therebyexperience the same or substantially the same transverse forcecomponents from adjacent ions, these components acting in oppositedirections, thereby substantially nullifying each other. The resultantion motion, therefore, is substantially solely radial.

In the following will be described at least two different, practicalworking embodiments of this invention, whereby the ideal conditions ofion input may be approached, thereby resulting in greater efiicienciesin fusor operation. Continuing with the embodiment of FIG. 1, potentialsare applied to the various electrodes 20, 21 and 22 in accordance withthe potential distribution illustrated by the graph of FIG. 2. With theanode 21 hermetically sealed and containing fusion reacting gas, such asdeuterium or deuterium-tritium, at a pressure of the order of to 10*torr, electrons from the cathode 29 will be attracted toward and throughthe ion-source grid 22, which is more positive than the anode 21. Thoseelectrons which are not collected by the grid 22 pass through theopenings thereof into the space thereinside where they encounter themore negative potential of the cathode 20. This results in the electronsbeing turned backwardly toward the grid 22, where once again most ofthem penetrate the openings thereof and pass beyond. Upon passingthrough, they immediately encounter the attraction of the grid 22, suchthat they return once again toward the grid 22, passing through theopenings therein if they are not collected. As will now be appreciated,the electrons in many cases make repeated oscillatory passes through themeshes of the grid 22 before they are eventually collected.Representative paths followed by these electrons are indicated by theserpentine dashed lines 35, which tend to fill in the entire sphericalextent of the grid 22. These electrons as well as those produced in theprocess of ionization and those produced by secondary processes onanodes 21 result in the formation of an electron cloud in sheath orshell-like form which clothes or otherwise submergcs the grid 22.Neutral gas within the vicinity of this cloud is ionized by theelectrons therein, thereby producing the ions 31 previously described.

Ions impacting the cathode will produce secondary electrons which falloutwardly toward the more positive potential of the grid 22. Theseelectrons, if not collected by the grid 22, pass through the openingsthereof and impact the anode 21, once again releasing secondaries whichare attracted back toward the grid 22. These electrons contribute to theformation of the cloud at the grid 22 and ionization previouslyexplained.

Since the electron cloud is also spherical in shape as is the grid 22,ionization will occur throughout this spherical extent. The ions 31 maythereupon be regarded as emanating from an area source of sphericalshape rather than from a point source as is true in certain prior artdevices.

A working embodiment of the arrangement just described in connectionwith FIG. 1 is shown in FIG. 3, in which the anode is a stainless steelshell and the cathode 20 and grid 22 are in the form of self-supportingcages made of tantalum or the like wire arranged like latitudes andlongitudes on a sphere. The intersections of the wires are spot-weldedso as to make each shell or cage 20 and 22 self-supporting and rigid.The openings in the cages are large, in one instance being aboutone-fifth the diameter of the respective cage. The grid 22 is fixedlypositioned concentrically inside the anode 21 by means of a conductivesupporting bar 36 which is held in place by means of a feed-throughinsulator 37 secured to an opening 38 in the anode 21. This supportingbar 36 constitutes the electrical connection to the grid 22.

A similar supporting bar 39 is secured to the cathode 20 and is rigidlysecured in place by means of another feed-through insulator 40 rigidlysecured to the anode 21, this bar 39 passing through an opening 41 inthe anode. The grid 22 has an opening 42 in the upper end thereofthrough which the bar 39 passes, the size of this opening 42 being suchas to provide adequqate insulation against accidental arcing between thebar 39 and the grid 22 due to the high voltages applied thereto.

The annular, thermionic cathode 29 is fixedly mounted in the illustratedposition by means of the supporting straps 43 secured in place withrespect to the anode 21. The bar 43a enclosed in the feed-throughinsulator 44- constitutes one connection to the heater inside thecathode 29, the other connection to the heater being grounded to theanode 21 shell. The cathode 29 is concentrically positioned with respectto both the grid 22 and the anode 21 as shown. To an opening in thebottom of the shell 21 is secured a tubular connection 45 to which maybe connected a vacuum pump for scavenging unwanted gases from theinterior of the anode 21. The latter is hermetically sealed.

In the operation of this embodiment of FIG. 3, the anode 21 is evacuatedand controlled amounts of fusion gases are admitted thereto untildesired pressures are reached. By way of example, gas pressures in thevicinity of 10" to 10" torr have been found to provide an operativedevice. Typical operating voltages applied to the various electrodes areindicated in FIGS. 1 and 2. Adjustment of the voltage applied to thegrid 22 and adjustment of the gas pressure determines in large measurethe magnitude of the ion current to the cathode 20.

In FIGS. 4 through 7 are illustrated a second embodiment of thisinvention which is primarily cylindrical rather than spherical as istrue of the arrangement of FIG. 3. Like numerals with the suffix lettera will indicate like parts. The cathode 20a and ion-source 22a arecylindrical and formed of wire with substantial spacing therebetween.The structure thereof will appear essentially the same as that of thespheres 20 and 22 in FIG. 3. The opposite ends of the cathode 20a andgrid 22a are formed as hemispheres as shown so as to maintain equalspacing and shapes between the two electrodes around the entireperipheries thereof.

The anode 21a is generally a cylindrical shell of stainless steel or thelike having a vacuum pump connection 45a at the bottom thereof and capassemblies 46 on the opposite ends which serve to seal hermetically theanode 21a and provide for mounting the various internal electrodes aswill be described. The cathode 20a is fixedly held in position by meansof a supporting bar 39a of a feed-through insulator 40a. The bar 39apasses through an insulating opening 42a in the ion-source grid 22a asshown. A metal disc 47 is secured to the anode shell 21a inside theopening 41a for substantially closing the same with the exception of theprovision of an insulating opening 48 surrounding the supporting bar39a.

The ion-source grid 22a is supported at both ends by means offeed-through insulators 49 having insulators portions secured to the capassemblies 4-6 and conductive supporting bars 50 secured to the grid 22aby means of welding or the like as shown. The mountings for this grid22a are rigid so as to maintain the proper positioning of the grid withrespect to the anode and cathode.

In the opposite ends of the anode 21a are provided two metallic endbells or hemispheres 51 equally spaced from and substantially concentricwith respect to the ends of the cathode 20a and grid 22a. Eachhemisphere 51 forms a part of the anode 21a and is held in position bymeans of a short length of metal tubing 52 secured at one end to thehemisphere 51 and at the other end to the cap assembly 46 as shown. Thecentral portion of the hemisphere 51 is provided with an aperture 53through which the interior of the fusor may be view-ed.

Extending coaxially from each cap assembly 46 is a viewing-tube assembly54 closed by a Brewster angle window for diagnostic studies. It will beunderstood that all of these parts are fitted together so as tohermetically seal the device such that the interior of the anode 21a canbe evacuated and the pressure thereinside controlled.

The bars 50 which mount the grid 22a are insulated from the respectivehemispheres 51 by means of ceramic sleeves 56.

Inside each hemisphere 51 is mounted a thermionic cath ode 29a, thiscathode being a part of an assembly composed of an annular mountingplate 58 spot-welded to the respective hemisphere 51 in coaxial relationtherewith. To the inner edge of the plate 58 is secured a short focusingcylinder 59 which extends along the cylindrical axis but is spaced fromthe grid 22a as shown. Surrounding the focusing cylinder 59 and mountedon the plate 58 is the annular cathode 29a of conventional design whichcontains an electrical heater having leads to which is connected thefilament supply. As explained earlier, and as shown diagrammatically inFIG. 5, one of these leads is grounded to the anode 21a while the otherlead penetrates the anode 21a via a feed-through insulator forconnection to the other side of the filament supply. As shown, thefilament 29a is fastened to the mounting plate 58 by means of suitablemetallic posts 60.

The operation of the arrangement of FIG. 4 is best explained byreferring to FIG. 7. With the interior of the hermetically sealed anode21a properly evacuated and a suitable quantity of fusion gasthereinside, electrons from the cathodes 29a follow serpentine pathsthrough the meshes of the grid 22a, thereby contributing to ionizationof neutral gas and the eventual formation of the electron cloud whichshrouds the grid 22a as previously explained. Ions 31a follow the radialpaths 32a toward the center of the device which in this case is the axis30a. In cross-section, this arrangement of FIG. 7 will appear exactlylike that shown in FIG. 1; however, in longitudinal section, the ions31a will follow essentially parallel paths which define planes normal tothe axis 30a. Those ions formed in the curved ends of the device willalso be focused inwardly toward the axis 30a but at angles to the planesjust described.

Inasmuch as all ions are directed toward a cross-over on the axis 30a,certain of such ions will collide, producing fusion reactions. Both theanode and grid voltages may be adjusted to secure optimum operation.

A third embodiment of this invention essentially the same as that ofFIG. 4 is of an annular or toroidal shape, the anode 21a being formedinto a circle or doughnut shape in which the ends 46 merge. In thisembodiment, the anode 21a would appear as a doughnut having a hollowannular interior, the cathode a and the grid 22a having similar shapethereinside. In this case, there would be no closed ends on any of theseelectrodes; however, in cross-section the structure would appear almostexactly as shown in FIG. 1. In this geometry, the cathodes 29a would belocated adjacent to anode 21a but outside of anode 22a. The operationwould be essentially the same as already described.

In a working embodiment of this invention as shown in FIG. 3, various ofthe components are of the following dimensions, these being given by wayof example only since such dimensions may be changed without departingfrom the concept of this invention:

Inches Anode 21 diameter 6 Ion cage 22 diameter 4 /2 Cathode 20 diameter1 /2 While there have been described above the principles of thisinvention in connection with specific apparatus, it is to be clearlyunderstood that this description is made only by Way of example and notas a limitation to the scope of the invention.

What is claimed is:

1. Apparatus for generating fusion reactions comprising anode means,cathode means inside said anode means, ion-source means spaced from anddisposed between said anode and cathode means, said cathode meansdefining a volume centrally located with respect to all of said anode,ion-source and cathode means, said volume being free of tangiblestructure, means for applying potentials to said anode, ion-source andcathode means for establishing a first electric field in the first spacebetween said anode and ion-source means and a second electric field inthe second space between said ion-source and said cathode means, saidion-source means being of positive potential with respect to said anodeand cathode means, said second electric field being of sufficientmagnitude to impart fusion-reacting energies to particles of positivecharge introduced into said second space, both said ionsource andcathode meansbeingpermeable to charged particle and gas fiow, meansproviding electrons in said second space adjacent to said ion-sourcemeans which ionizes neutral gas therein, means including said anode,ion-source and cathode means for focusing ions inside said ion-sourcemeans toward the center of said volume, and means for introducing intoand controlling amounts of gas into said first space.

2. The apparatus of claim 1 in which said anode, said ion-source andcathode means are of circular shape in cross-section and concentricallypositioned with respect to each other.

3. The apparatus of claim 2 in which said anode means is essentially asolid hermetically sealed metallic shell, and each of said ion-sourcemeans and said cathode means is a self-supporting conductive electrodehaving a multiplicity of openings therein through which gas and ions mayfreely flow.

4. The apparatus of claim 3 in which said electron means is a thermioniccathode disposed in said first space adjacent to said ion-sourceelectrode, whereby electrons emitted by said thermionic cathode areattracted toward said ion-source electrode instead of said anode shell.

5. The apparatus of claim 4 in which said anode shell and saidelectrodes are spherically shaped, said thermionic cathode is of annularshape and concentrically dis posed about a diameter of said anode shell,said thermionic cathode having two supply leads of which one is groundedto said anode shell and the other passes through the latter inhermetically sealed insulated relation.

6. The apparatus of claim 5 in which said electrodes are each fabricatedof wires spaced apart and interconnected so so to provide a foraminousstructure in which the openings have dimensions about one-fifth thediameter of the particular electrode, said anode shell having a vacuumpump connection by means of which the anode shell can be evacuated andcontrolled quantities of gas can 'be admitted thereto.

7. The apparatus of claim 4 in which said anode shell and saidelectrodes are cylindrically shaped, the opposite ends of each of saidanode shell and said electrodes being hemispherically shaped, therebeing two such thermionic cathodes which are of annular shape, thesecathodes being coaxial with respect to the axis of said anode shell withone at each end of said ion-source electrode.

8. The apparatus of claim 7 in which said electrodes are each fabricatedof wires spaced apart and interconnected so as to provide a foraminousstructure, and means for focusing electrons emitted by said thermioniccathodes toward said ion-source electrode in the portion thereof whichis cylindrical.

9. The apparatus of claim 8 in which the length of the diameter of saidthermionic cathodes is between the lengths of the diameters of saidion-source and cathode electrodes, said focusing means including afocusing cylinder disposed coaxially inside each thermionic cathode.

References Cited UNITED STATES PATENTS 6/1966 Farnsworth 1761 6/1968Farnsworth 1761

